#! ruby
# yukicoder My Practice
# author: Leonardone @ NEETSDKASU

x = gets.to_i

loop { d, m = x.divmod 4; if m != 0 then break else x = d end }

3.step(x ** 0.5, 2) do |k|
    kk = k * k
    if x < kk then break end
    loop { d, m = x.divmod kk; if m != 0 then break else x = d end }
end

puts x